1. Field of the Invention
The present invention relates to information transmission technologies, and in particular, to an active radio frequency identification (RFID) tag and an application system and method thereof.
2. Description of the Related Art
The existing active RFID tag mainly achieves long-distance identification and management for human being, objects, and vehicles. The basic working principles are: reading the ID of the active RFID tag installed on the target to be identified in radio frequency (RF) communication mode, and then invoking related information or data pre-stored the database of a control processor (for example, a computer) and corresponding to the ID to implement identification and management for a target. Therefore, application of such technology requires a connection to the related database of the control processor.
The current active RFID tag commonly works in a mode of initiatively and periodically transmitting its ID. To be specific, it is preset using an internal clock that the crystal oscillator and frequency synthesizer in the active RFID tag are started at a specific interval (for example, 1 second, 5 seconds or 10 minutes) and data packet information having a specific length is transmitted. For power saving, generally the short ID information is transmitted only, and then the active RFID tag enters the dormant state. In the dormant state, only the internal clock of the tag is running. This reduces the working time of the system and somehow prolongs the life cycle of the battery. However, this method also produces some problems, such as electromagnetic pollution to the environment, signal congestion and mutual interference, lack of working flexibility and adaptability.
The patent application No. 200710196801.X discloses an intelligent RFID tag system, using bidirectional communication, reducing electromagnetic pollution to the environment, signal congestion and mutual interference. However, when the active RFID tag, after periodical wakeup, identifies short signals transmitted by a semaphore, the active RFID tag performs software identification for a plurality of invalid received signals to determine whether theses signals are the desired short information. This, however, consumes a large amount of electric power of the active RFID tag.
After a low-frequency instruction signal is detected using a low-frequency detection circuit, the crystal oscillator and frequency synthesizer in a high-frequency transceiver are started to enable the high-frequency transceiver to enter the state of receiving and transmitting signals. Although the system consumes no electric power before the detection circuit detects the instruction signal, since the sensitivity of the low-frequency detection circuit is generally very low, the low-frequency detection circuit is capable of detecting signals within a short distance. It is still hard to increase the wakeup distance by improving the transmit power of the low-frequency signals. Consequently, the active RFID tag working in low-frequency detection circuit wakeup mode, achieves signal read and write only within a limited distance, is large in size, and lacks flexibility. Moreover, the system cost is high. As a result, the application of such type of active RFID tag is very limited.
To supplement the functions of the RFID tag, and enhance the flexibility, some active RFID tags adopt a method where the high-frequency and low-frequency communication systems work simultaneously. For example, two transceiver systems using a low frequency of 125 kHz and a high frequency of 2.4 GHz; in some active RFID tags, two transceiver systems using an ultra wideband (UWB) and a high frequency of 2.4 GHz. In this way, the complexity and cost of the RFID tag are increased, and the functions of the RFID tag is very limited.
The existing active RFID tag generally works in narrowband single frequency mode. In narrowband single frequency mode, the active RFID tag is easily subject to external interference. In addition, due to changes of the temperature, the working frequency of the crystal oscillator shifts out of aging, and in the actual application, the multipath effect and the Doppler effect may severely affect the reliability and stability of the system, especially in the industrial field with strong interference and in the scenario where the target to be identified is fast moving.
The existing active RFID tag is as what is stated in a recent document released (on March, July, and September 2009) by the IEEE Active RFID Tag International Standard Working Group: “Most active tags today in the market use a simplex (one-way) ID transmission scheme for the sole purpose of determining location in order to reduce their energy consumption and have no congestion control mechanism for high density reads. Active RFID tags require the ability to provide bidirectional communications as well as ranging, and congestion control for high density reads using ultra-low power. There are no international standards that meet this need.”
With the proposal of the Internet of Things, people desire to make use of the advantages, such as simple structure, small size, low cost, and low power consumption, of the active RFID tag to address the issue during information transmission on the Internet of Things on how to establish a simple but reliable, cost-effective and low power consuming radio communication between people or objects and the public communication network within several meters to almost a thousand meters. This requires that the active RFID tag have the bidirectional communication capability adaptive to on demand working, more strong working adaptability and flexibility.
Further, with the proposal of the Internet of Things, people desire to make use of the advantages, such as simple structure, small size, low cost, and low power consumption, of the active RFID tag to address the issue during information transmission on the Internet of Things on how to establish a simple but reliable, cost-effective and low power consuming radio communication between people or objects and the public communication network within several meters to almost a thousand meters. Through such communication, identification information and state information (information of the tag and sensor) of related people and object may be quickly transmitted to a related control center. This presents a great challenge to the active RFID tag. Besides requirements of low power consumption, low cost, and working flexibility, it is also a critical issue on how to solve the problem of signal congestion. Although the bidirectional communication mode can be used to enable the active RFID tag to work on demand, during processing of mass tag information, it is obviously crucial to improve the air communication efficiency while reducing the time for air communication as much as possible. Especially, the information transmission on the Internet of Things is much more complex than the common identification application where only an ID is transmitted. During the information transmission on the Internet of Things, the two parties involved in the communication may need to repeat the transmission multiple times before completing a simple task; in addition, the more information transmitted each time, the high the probability of error and retransmission. This not only consumes more electric power, but also occupies more time of an air channel in the critical moment and place, thereby increasing congestion in the air communication and causing possible mutual interference. Therefore, it is important to shorten the time for air communication.